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// Copyright 2013 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package ir
// Helpers for emitting IR instructions.
import (
"fmt"
"go/ast"
"go/constant"
"go/token"
"go/types"
)
// emitNew emits to f a new (heap Alloc) instruction allocating an
// object of type typ. pos is the optional source location.
//
func emitNew(f *Function, typ types.Type, source ast.Node) *Alloc {
v := &Alloc{Heap: true}
v.setType(types.NewPointer(typ))
f.emit(v, source)
return v
}
// emitLoad emits to f an instruction to load the address addr into a
// new temporary, and returns the value so defined.
//
func emitLoad(f *Function, addr Value, source ast.Node) *Load {
v := &Load{X: addr}
v.setType(deref(addr.Type()))
f.emit(v, source)
return v
}
func emitRecv(f *Function, ch Value, commaOk bool, typ types.Type, source ast.Node) Value {
recv := &Recv{
Chan: ch,
CommaOk: commaOk,
}
recv.setType(typ)
return f.emit(recv, source)
}
// emitDebugRef emits to f a DebugRef pseudo-instruction associating
// expression e with value v.
//
func emitDebugRef(f *Function, e ast.Expr, v Value, isAddr bool) {
if !f.debugInfo() {
return // debugging not enabled
}
if v == nil || e == nil {
panic("nil")
}
var obj types.Object
e = unparen(e)
if id, ok := e.(*ast.Ident); ok {
if isBlankIdent(id) {
return
}
obj = f.Pkg.objectOf(id)
switch obj.(type) {
case *types.Nil, *types.Const, *types.Builtin:
return
}
}
f.emit(&DebugRef{
X: v,
Expr: e,
IsAddr: isAddr,
object: obj,
}, nil)
}
// emitArith emits to f code to compute the binary operation op(x, y)
// where op is an eager shift, logical or arithmetic operation.
// (Use emitCompare() for comparisons and Builder.logicalBinop() for
// non-eager operations.)
//
func emitArith(f *Function, op token.Token, x, y Value, t types.Type, source ast.Node) Value {
switch op {
case token.SHL, token.SHR:
x = emitConv(f, x, t, source)
// y may be signed or an 'untyped' constant.
// TODO(adonovan): whence signed values?
if b, ok := y.Type().Underlying().(*types.Basic); ok && b.Info()&types.IsUnsigned == 0 {
y = emitConv(f, y, types.Typ[types.Uint64], source)
}
case token.ADD, token.SUB, token.MUL, token.QUO, token.REM, token.AND, token.OR, token.XOR, token.AND_NOT:
x = emitConv(f, x, t, source)
y = emitConv(f, y, t, source)
default:
panic("illegal op in emitArith: " + op.String())
}
v := &BinOp{
Op: op,
X: x,
Y: y,
}
v.setType(t)
return f.emit(v, source)
}
// emitCompare emits to f code compute the boolean result of
// comparison comparison 'x op y'.
//
func emitCompare(f *Function, op token.Token, x, y Value, source ast.Node) Value {
xt := x.Type().Underlying()
yt := y.Type().Underlying()
// Special case to optimise a tagless SwitchStmt so that
// these are equivalent
// switch { case e: ...}
// switch true { case e: ... }
// if e==true { ... }
// even in the case when e's type is an interface.
// TODO(adonovan): opt: generalise to x==true, false!=y, etc.
if x, ok := x.(*Const); ok && op == token.EQL && x.Value != nil && x.Value.Kind() == constant.Bool && constant.BoolVal(x.Value) {
if yt, ok := yt.(*types.Basic); ok && yt.Info()&types.IsBoolean != 0 {
return y
}
}
if types.Identical(xt, yt) {
// no conversion necessary
} else if _, ok := xt.(*types.Interface); ok {
y = emitConv(f, y, x.Type(), source)
} else if _, ok := yt.(*types.Interface); ok {
x = emitConv(f, x, y.Type(), source)
} else if _, ok := x.(*Const); ok {
x = emitConv(f, x, y.Type(), source)
} else if _, ok := y.(*Const); ok {
y = emitConv(f, y, x.Type(), source)
//lint:ignore SA9003 no-op
} else {
// other cases, e.g. channels. No-op.
}
v := &BinOp{
Op: op,
X: x,
Y: y,
}
v.setType(tBool)
return f.emit(v, source)
}
// isValuePreserving returns true if a conversion from ut_src to
// ut_dst is value-preserving, i.e. just a change of type.
// Precondition: neither argument is a named type.
//
func isValuePreserving(ut_src, ut_dst types.Type) bool {
// Identical underlying types?
if structTypesIdentical(ut_dst, ut_src) {
return true
}
switch ut_dst.(type) {
case *types.Chan:
// Conversion between channel types?
_, ok := ut_src.(*types.Chan)
return ok
case *types.Pointer:
// Conversion between pointers with identical base types?
_, ok := ut_src.(*types.Pointer)
return ok
}
return false
}
// emitConv emits to f code to convert Value val to exactly type typ,
// and returns the converted value. Implicit conversions are required
// by language assignability rules in assignments, parameter passing,
// etc. Conversions cannot fail dynamically.
//
func emitConv(f *Function, val Value, typ types.Type, source ast.Node) Value {
t_src := val.Type()
// Identical types? Conversion is a no-op.
if types.Identical(t_src, typ) {
return val
}
ut_dst := typ.Underlying()
ut_src := t_src.Underlying()
// Just a change of type, but not value or representation?
if isValuePreserving(ut_src, ut_dst) {
c := &ChangeType{X: val}
c.setType(typ)
return f.emit(c, source)
}
// Conversion to, or construction of a value of, an interface type?
if _, ok := ut_dst.(*types.Interface); ok {
// Assignment from one interface type to another?
if _, ok := ut_src.(*types.Interface); ok {
c := &ChangeInterface{X: val}
c.setType(typ)
return f.emit(c, source)
}
// Untyped nil constant? Return interface-typed nil constant.
if ut_src == tUntypedNil {
return emitConst(f, nilConst(typ))
}
// Convert (non-nil) "untyped" literals to their default type.
if t, ok := ut_src.(*types.Basic); ok && t.Info()&types.IsUntyped != 0 {
val = emitConv(f, val, types.Default(ut_src), source)
}
f.Pkg.Prog.needMethodsOf(val.Type())
mi := &MakeInterface{X: val}
mi.setType(typ)
return f.emit(mi, source)
}
// Conversion of a compile-time constant value?
if c, ok := val.(*Const); ok {
if _, ok := ut_dst.(*types.Basic); ok || c.IsNil() {
// Conversion of a compile-time constant to
// another constant type results in a new
// constant of the destination type and
// (initially) the same abstract value.
// We don't truncate the value yet.
return emitConst(f, NewConst(c.Value, typ))
}
// We're converting from constant to non-constant type,
// e.g. string -> []byte/[]rune.
}
// A representation-changing conversion?
// At least one of {ut_src,ut_dst} must be *Basic.
// (The other may be []byte or []rune.)
_, ok1 := ut_src.(*types.Basic)
_, ok2 := ut_dst.(*types.Basic)
if ok1 || ok2 {
c := &Convert{X: val}
c.setType(typ)
return f.emit(c, source)
}
panic(fmt.Sprintf("in %s: cannot convert %s (%s) to %s", f, val, val.Type(), typ))
}
// emitStore emits to f an instruction to store value val at location
// addr, applying implicit conversions as required by assignability rules.
//
func emitStore(f *Function, addr, val Value, source ast.Node) *Store {
s := &Store{
Addr: addr,
Val: emitConv(f, val, deref(addr.Type()), source),
}
// make sure we call getMem after the call to emitConv, which may
// itself update the memory state
f.emit(s, source)
return s
}
// emitJump emits to f a jump to target, and updates the control-flow graph.
// Postcondition: f.currentBlock is nil.
//
func emitJump(f *Function, target *BasicBlock, source ast.Node) *Jump {
b := f.currentBlock
j := new(Jump)
b.emit(j, source)
addEdge(b, target)
f.currentBlock = nil
return j
}
// emitIf emits to f a conditional jump to tblock or fblock based on
// cond, and updates the control-flow graph.
// Postcondition: f.curre
8000
ntBlock is nil.
//
func emitIf(f *Function, cond Value, tblock, fblock *BasicBlock, source ast.Node) *If {
b := f.currentBlock
stmt := &If{Cond: cond}
b.emit(stmt, source)
addEdge(b, tblock)
addEdge(b, fblock)
f.currentBlock = nil
return stmt
}
// emitExtract emits to f an instruction to extract the index'th
// component of tuple. It returns the extracted value.
//
func emitExtract(f *Function, tuple Value, index int, source ast.Node) Value {
e := &Extract{Tuple: tuple, Index: index}
e.setType(tuple.Type().(*types.Tuple).At(index).Type())
return f.emit(e, source)
}
// emitTypeAssert emits to f a type assertion value := x.(t) and
// returns the value. x.Type() must be an interface.
//
func emitTypeAssert(f *Function, x Value, t types.Type, source ast.Node) Value {
a := &TypeAssert{X: x, AssertedType: t}
a.setType(t)
return f.emit(a, source)
}
// emitTypeTest emits to f a type test value,ok := x.(t) and returns
// a (value, ok) tuple. x.Type() must be an interface.
//
func emitTypeTest(f *Function, x Value, t types.Type, source ast.Node) Value {
a := &TypeAssert{
X: x,
AssertedType: t,
CommaOk: true,
}
a.setType(types.NewTuple(
newVar("value", t),
varOk,
))
return f.emit(a, source)
}
// emitTailCall emits to f a function call in tail position. The
// caller is responsible for all fields of 'call' except its type.
// Intended for wrapper methods.
// Precondition: f does/will not use deferred procedure calls.
// Postcondition: f.currentBlock is nil.
//
func emitTailCall(f *Function, call *Call, source ast.Node) {
tresults := f.Signature.Results()
nr := tresults.Len()
if nr == 1 {
call.typ = tresults.At(0).Type()
} else {
call.typ = tresults
}
tuple := f.emit(call, source)
var ret Return
switch nr {
case 0:
// no-op
case 1:
ret.Results = []Value{tuple}
default:
for i := 0; i < nr; i++ {
v := emitExtract(f, tuple, i, source)
// TODO(adonovan): in principle, this is required:
// v = emitConv(f, o.Type, f.Signature.Results[i].Type)
// but in practice emitTailCall is only used when
// the types exactly match.
ret.Results = append(ret.Results, v)
}
}
f.Exit = f.newBasicBlock("exit")
emitJump(f, f.Exit, source)
f.currentBlock = f.Exit
f.emit(&ret, source)
f.currentBlock = nil
}
// emitImplicitSelections emits to f code to apply the sequence of
// implicit field selections specified by indices to base value v, and
// returns the selected value.
//
// If v is the address of a struct, the result will be the address of
// a field; if it is the value of a struct, the result will be the
// value of a field.
//
func emitImplicitSelections(f *Function, v Value, indices []int, source ast.Node) Value {
for _, index := range indices {
fld := deref(v.Type()).Underlying().(*types.Struct).Field(index)
if isPointer(v.Type()) {
instr := &FieldAddr{
X: v,
Field: index,
}
instr.setType(types.NewPointer(fld.Type()))
v = f.emit(instr, source)
// Load the field's value iff indirectly embedded.
if isPointer(fld.Type()) {
v = emitLoad(f, v, source)
}
} else {
instr := &Field{
X: v,
Field: index,
}
instr.setType(fld.Type())
v = f.emit(instr, source)
}
}
return v
}
// emitFieldSelection emits to f code to select the index'th field of v.
//
// If wantAddr, the input must be a pointer-to-struct and the result
// will be the field's address; otherwise the result will be the
// field's value.
// Ident id is used for position and debug info.
//
func emitFieldSelection(f *Function, v Value, index int, wantAddr bool, id *ast.Ident) Value {
fld := deref(v.Type()).Underlying().(*types.Struct).Field(index)
if isPointer(v.Type()) {
instr := &FieldAddr{
X: v,
Field: index,
}
instr.setSource(id)
instr.setType(types.NewPointer(fld.Type()))
v = f.emit(instr, id)
// Load the field's value iff we don't want its address.
if !wantAddr {
v = emitLoad(f, v, id)
}
} else {
instr := &Field{
X: v,
Field: index,
}
instr.setSource(id)
instr.setType(fld.Type())
v = f.emit(instr, id)
}
emitDebugRef(f, id, v, wantAddr)
return v
}
// zeroValue emits to f code to produce a zero value of type t,
// and returns it.
//
func zeroValue(f *Function, t types.Type, source ast.Node) Value {
switch t.Underlying().(type) {
case *types.Struct, *types.Array:
return emitLoad(f, f.addLocal(t, source), source)
default:
return emitConst(f, zeroConst(t))
}
}
func emitConst(f *Function, c *Const) *Const {
f.consts = append(f.consts, c)
return c
}